The invention relates to light sources, and more particularly to light sources requiring a substantially uniform illumination area.
Many optical devices, such as indicators on a car""s dashboard, microdisplays in electronic cameras and other types of display, require illumination by a beam of light having relatively uniform brightness. However, most light sources, such as incandescent lights, arc lamps, and light emitting diodes, provide a nonuniform light output that is unsuitable for direct use.
One approach to uniformizing the light produced by the light source is to couple the light from the light source into a light diffusing cavity. The light diffusing cavity typically has diffusely reflecting walls, which results in diffusing and mixing the light from the light source. The light exits the cavity through a transmitting surface with a substantially uniform brightness.
A common approach to forming a diffusing cavity is to use a metallic parabola, or cavity, whose inner surface is coated with a reflective metal or white diffuse material. A transmitting film is attached to the output from the parabola, or cavity, as the transmitting surface. Coating the metallic component and attaching the transmitting film is labor intensive process, and requires a particularly high level of skill and equipment where the metallic cavity and transmitting film are only a few millimeters in size, as is typical with microdisplays.
Therefore, there is a need for an improved diffusing cavity which reduces the time and effort required for assembly.
Generally, the present invention relates to a cavity for diffusing light from a light source so as to produce a uniform light output. The cavity is formed from a unitary structure having one or more portions that diffusely reflect light within the cavity and another portion that transmits the uniform light output.
One particular embodiment of the invention is a unitary structure, formed from an optically diffusive material, that defines a diffusing cavity having an access aperture. A portion of the unitary structure defines diffusely reflective walls and another portion of the unitary structure defines a diffusely transmitting screen. A portion of the diffusely reflecting walls has a portion that has a thickness being greater than a thickness of the diffusely transmitting screen.
In another embodiment of the invention, a light diffusing device includes a unitary structure formed from an optically diffusive material. The unitary structure defines a diffusing cavity having an access aperture. A first portion of the unitary structure substantially diffusely reflects and mixes light within the diffusing cavity. A second portion of the unitary structure substantially diffusely transmits light from the diffusing cavity as a light output.
Another embodiment of the invention is an illuminated display device, which includes a light source and a light diffuser. The light diffuser is formed from a first material and defines diffusely reflecting walls and a diffusely transmitting screen. The diffusely reflecting walls and transmitting screen are formed as a unitary body and define a diffuser cavity having an access aperture. A wall thickness is greater than a transmitting screen thickness. Light from the light source is diffusely reflected within the cavity and is diffusely transmitted through the transmitting screen to illuminate an imaging device which imposes an image on light received from the light diffuser.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.